1. Field of the Invention
Mixing two materials.
2. Review of the Prior Art
The following definitions will be used in this application.
Pulping is the changing of wood chips or other wood particulate matter to fibrous form. Chemical pulping requires cooking of the chips in solution with a chemical, and includes partial removal of the coloring matter such as lignin associated with the wood.
Bleaching is the treatment of cellulosic fibers to remove or alter the coloring matter associated with the fibers to allow the fiber to reflect white light more truly.
Researchers attempting to add oxygen into the pulping process, or to replace portions of the system with oxygen processing, had a number of concerns. A continuing concern was the poor solubility of oxygen in water and its poor transference from the gas to the liquid phase and into the fiber. The usual solutions to these problems have been high pressures, high oxygen concentrations, and particular vessel configurations to promote the transfer of oxygen into the fiber.
Another concern was the degradation of the pulp by the oxygen. The solution to this problem was a protector of some kind. There are a number of patents which describe various protectors that might be used. Exemplary are Robert et al., U.S. Pat. No. 3,384,533, issued May 21, 1968; Noreus et al., U.S. Pat. No. 3,652,386, issued Mar. 28, 1972; and Smith et al., U.S. Pat. No. 3,657,065, issued Apr. 18, 1972.
There has also been a concern about channeling of the oxygen in the system and various ways to prevent channeling have been proposed. The Roymoulik et al. U.S. Pat. No. 3,832,276, issued Aug. 27, 1974, and Phillips U.S. Pat. No. 3,951,733, issued Apr. 20, 1976, note this problem and suggest solutions.
A great deal of art describes both oxygen bleaching of pulp or refining of pulp. The following patents and articles are exemplary.
The first is Laakso U.S. Pat. No. 4,002,528, which issued Jan. 11, 1977. This patent describes an environment for the present invention--two refiners 34 and 35 within the blow line 32 between digester 24 and a storage or blow tank 38.
The Kamyr blow line oxygen system is described in Richter, U.S. Pat. No. 3,963,561, issued June 15, 1976, and in Kleppe et al "Oxygen Alkali Delignification at Kamyr Digester Blow Line Consistency--status report," 1976 International Pulp Bleaching Conference, May 2-6, 1976, TAPPI November 1976, Vol. 59, No. 11, pp. 77-80. In this system, oxygen is added to the pulp in the blow line between the digester and the oxygen reactor. The oxygen is added just prior to a refiner located at the bottom of the reactor. The pulp is at a consistency of 5-20% and preferably 8-12%. The reactor is of an upflow-downflow type in which the pulp and oxygen are carried upward in a conical inner section of the reactor and flow downward in the outer section of the reactor. The pulp must remain in the inner upflow section of the reactor for from 20-30 minutes, allowing the pulp to become 90% oxidized. In the pilot plant the retention time in the inner upflow section of the reactor was 40 minutes.
The patent and article disclose a number of mechanical features within the reactor to keep the pulp from floating to the top and to ensure that the pulp remains within the conical inner section of the reactor the appropriate length of time. The patent is directed to the reuse of the excess oxygen within the system. The article describes this system in use at the Moss Norway plant.
The Rauma-Repola system is described in the Federal Republic of Germany patent disclosure No. 24 41 579, Mar. 13, 1975 and in Yrjala, et al., New Aspects in Oxygen Bleaching, dated Apr. 18, 1974. The system uses the Vortex mixer shown in FIGS. 2 and 3. Using either a number of passes through a single mixer or several mixers in series, it is possible to bleach the pulp in from 5 to 15 minutes. The consistency is 3%.
Richter U.S. Pat. No. 4,093,506, issued June 6, 1978, describes a mixer for mixing bleaching fluids such as chlorine or chlorine dioxide with a high-consistency pulp. Rapidly rotating rotor blades essentially fluidize the pulp and the treatment gas is added to it then. The Kamyr reactor is also described in an article, "Pilot and Commercial Results of Medium Consistency Chlorination" given at the Bleaching Seminar on Chlorination and Caustic Extraction, Nov. 10, 1977 in Washington, D.C.
Reinhall U.S. Pat. No. 4,082,233, issued Apr. 4, 1978, discloses a refiner having means for removing excess gas before the stock enters the refiner.